The present invention relates to use of alkali metal hydrogen phosphates as precursors in the synthesis of phosphate-containing electrochemical active materials, and methods of preparing alkali metal hydrogen phosphates.
A rechargeable or xe2x80x9csecondaryxe2x80x9d battery typically consists of one or more electrochemical cells, wherein each cell typically includes a cathode, an anode, and a liquid electrolyte or other material interposed there between for facilitating movement of ionic charge carriers between the anode and cathode. As the cell is charged, cations are removed from the cathode material and are deposited on and/or inserted into the anode. During discharge, cations migrate from the anode to the electrolyte and, in turn, from the electrolyte to the cathode.
Such batteries generally include insertion or xe2x80x9cintercalationxe2x80x9d electrodes containing materials that have a crystal lattice structure or framework into which ions can be inserted or intercalated, and subsequently extracted.
Alkali metal-containing phosphates (e.g. lithium phosphates), in particular, are desirable electrode materials because they have a higher initial electrical capacity (Axc2x7hr/g) than typical transition metal chalcogenide cathode active materials, and a low capacity loss throughout the life of the electrochemical cell.
The inventors of the present invention have found that alkali metal hydrogen phosphates, and in particular lithium hydrogen phosphates, exhibit a higher reactivity than other precursor compounds, contribute phosphate to the final alkali metal-containing phosphate active material product, eliminate undesirable by-products inherent in previously practiced synthesis routes, and yield active materials that exhibit superior performance-related properties as compared to active materials synthesized using conventional reactants. Unfortunately, presently known methods of manufacturing alkali metal hydrogen phosphates are not commercially viable, particularly for production of a battery active precursor material, due to difficulty in controlling reagents, incomplete reaction, inefficient utilization of reactor volume, failure to yield a homogenous reaction product, and reduced yield.
The present invention provides a cathode active material formed by a reaction of one or more suitable metal-containing compounds with an alkali metal hydrogen phosphate of the general formula AxH3xe2x88x92xPO4, wherein 0xe2x89xa6xxe2x89xa63, preferably 0xe2x89xa6xxe2x89xa63; and A is an alkali metal.
In one embodiment, the cathode active material is formed by a reaction of one or more suitable metal-containing compounds with a lithium hydrogen phosphate of the general formula LixH3xe2x88x92xPO4, where 0xe2x89xa6xxe2x89xa63, preferably 0xe2x89xa6xxe2x89xa63, and wherein the lithium hydrogen phosphate is prepared by admixing lithium carbonate, phosphoric acid, and water to form a mixture wherein the water in the mixture is at a level of from about 5% to about 25% by weight of the total mixture. A preferred method includes adding the water as a solvent for the phosphoric acid, and subsequently admixing this phosphoric acid solution to essentially dry lithium carbonate powder.
It has been found that when lithium hydrogen phosphate is employed as a reactant, the lithium hydrogen phosphate exhibits a higher reactivity than other precursor compounds, contributes phosphate to the final lithium metal phosphate active material product, eliminates undesirable by-products inherent in previously practiced synthesis routes, and yields active materials that exhibit superior performance-related properties as compared to active materials synthesized using conventional reactants.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. Thus, variations that do not depart from the general scope of the invention are intended to be within the scope of the invention.